The proposed study is designed to characterize, by in vitro methods, the collateral vessels that develop in response to chronic femoral artery occlusion with respect to anatomy, innervation, receptors and reactivity to naturally occurring vasoactive agents in an attempt to elucidate a possible stimulus for the selective growth of collaterals. These characteristics of collateral vessels will be compared to those of normal branch arteries of similar size from the same hypotensive extremity and from the unoccluded normotensive extremity during the period of active collateral growth and when collateral growth is complete. The following characteristics of collateral arteries, normotensive branch arteries and hypotensive branch arteries will be evaluated: 1. Wall thickness/lumen diameter ratio. 2. Smooth muscle mass, orientation of smooth muscle and number of elastic lamina. 3. Passive length-tension relationships under conditions of (a) normal smooth muscle tone and (b) complete smooth muscle relaxation. 4. Degree of innervation and relationship of nerve endings to smooth muscle fibers. 5. Characterization of nerve endings as adrenergic by means of tyramine, cocaine, and GD-131. 6. Characterization of adrenergic receptors as alpha or beta by means of norepinephrine, isoproterenol, phenoxybenzamine, practolol, and sotalol. 7. Response to norepinephrine, epinephrine, histamine, potassium, prostaglandin E1, E2 and F2 alpha, adenosine, hypoxia and hypercapnia.